Emily Watson has revealed she kept her German accent up between takes on The Book Thief because she was worried she would lose it.

The award-winning actress stars alongside Geoffrey Rush and Sophie Nelisse in the big-screen adaptation of Markus Zusak's novel The Book Thief, about life for a young girl growing up in Nazi Germany during the Second World War. Emily plays the girl's adoptive German mother Rosa Hubermann.

Emily revealed: "I think when you're playing somebody who's a long way away from who you are - I'm never quite sure I'll get back there.

"I find the accent thing - I have to stay in it to make it feel real. I'm not good enough, I don't think, to be able to flip in and out."

Although her character is introduced as mean and nagging, Emily said she could see an "inner goodness" in the brittle character.

"I was playing someone who was really angry and bitter and abusive, and really pretty mean and nasty. And yet she's married to this very sensitive, awake, poetic musician and painter, and you think, 'Those two things don't quite add up, so there's got to be some pretty interesting history there'," she said.

"I think she was young and beautiful once, and probably more soft-spoken, but the times have changed her."

And she revealed Geoffrey fitted easily into the role of Rosa's kind-hearted husband Hans.

Emily said: "He's one of life's natural clowns and he's a great raconteur. If you ever wanted to know where Geoffrey was on the set you'd just listen out for the laughter."

:: The Book Thief is in cinemas now.